1. Field of the Invention
The present invention relates to an image processing system for processing image signals, and more particularly, to an apparatus and method for expanding the dynamic range of a digital image signal in an image processing system.
2. Description of the Related Art
In image signal processing, much research has been conducted into reproducing an image taken by a camera to be close to the visual characteristics of a human being. The viewing range that a human being can perceive from a bright place to a dark place, that is, the dynamic range, is only about 120 dB. However, the dynamic range of an image processed by a general image processing system using a charge coupled device (CCD) is only about 60 db. Consequently, it is very difficult to obtain the same sensitivity as human vision from an image in which dark and bright luminance levels are mixed. Thus, the dynamic range of an image is expanded to overcome this problem.
U.S. Pat. No. 5,144,442 discloses one of the above-described conventional dynamic range expanding approaches for expanding the dynamic range of video. The disclosed conventional dynamic range expanding apparatus selects good-state parts from each video having a plurality of different exposure levels, and applies neighborhood transforms to the selected good-state parts, thereby expanding the dynamic range of a video. Here, the neighborhood transform is a type of image enhancement filtering. However, the above-described conventional dynamic range expanding apparatus must include a plurality of CCDs to simultaneously acquire a plurality of different videos.
In another conventional dynamic range expanding method used to address the problem, video signals having different exposure levels, which are adjacent to each other in terms of time, are combined. However, in this conventional dynamic range expanding method, in the case when an object included in an acquired image moves fast, when the images having different exposure levels are combined, the spacial positions of the objects in the images are mismatched. Therefore, the combined images are blurred. In order to solve this problem, a fast CCD capable of taking an image rapidly is required, but it is not easy to realize such a fast CCD in an image processing system using a camera.
An object of the present invention is to provide a dynamic range expanding apparatus capable of more stably expanding the dynamic range by removing motion blurring caused when images having different exposure levels are combined.
Another object of the present invention is to provide a dynamic range expanding method which is performed by the dynamic range expanding apparatus of an image processing system.
In one aspect, the present invention provides a dynamic range expanding apparatus in an image processing system for converting an analog video signal output from a charge coupled device into a digital video signal and expanding the dynamic range of the digital video signal. The apparatus of the invention includes a video multiplexing unit for dividing the digital video signal into an over-exposed video signal and an under-exposed video signal having different exposure levels. A motion correction unit corrects the moving part of an excessively-exposed video according to the amount of movement of an image acquired by the charged coupled device, using the output of the video multiplexing unit. A video output unit interpolates a dark part of a resultant signal corrected by the motion correction unit and a bright part of the under-exposed video signal using a luminance weight produced from the under-exposed video signal. The video output unit outputs the interpolated result as an expanded video signal having an expanded dynamic range.
The present invention also provides a dynamic range expanding method in an image processing system for converting an analog video signal output from a charge coupled device into a digital video signal and expanding the dynamic range of the digital video signal. In accordance with the method of the invention, the digital video signal is divided into an over-exposed video signal and an under-exposed video signal having different exposure levels. The moving part of an excessively-exposed video is corrected according to the amount of movement of an image acquired by the charged coupled device. A dark part of a resultant signal corrected in the motion correcting step and a bright part of the under-exposed video signal are interpolated using a luminance weight produced from the under-exposed video signal to determine the interpolated result as an expanded video signal having an expanded dynamic range.